Typically, during a normal operation of a washing machine, a user loads articles into a washer basket for cleansing, selects a wash cycle, and starts the machine. The washing machine then performs a number of operations to complete the wash cycle. Generally, the wash cycle includes a wash operation, a rinse operation and a spin operation. The wash operation includes filling the washer basket and a washer tub which contains the basket with a liquid such as water to a user selected level. An agitator disposed in the washer basket then imparts an oscillatory motion to the water and detergent (both the water and the detergent comprise the wash liquid) and the articles. The oscillatory motion causes the articles and wash liquid to move back and forth in the washer basket. This movement provides mechanical energy which assists in removing soils from the articles. After agitating the articles and wash liquid for a predetermined length of time, a pump pumps the liquid out of the washer basket and washer tub. The rinse operation is similar to the wash operation in that it includes filling the washer basket and the washer tub to a previously assigned level, agitating for a predetermined amount of time, and pumping the wash liquid out of the basket and tub. Typically, the wash cycle includes one wash operation and one rinse operation, but most washing machines provide an optional extra rinse operation to further remove any remaining detergent. Once a majority of the wash liquid has been removed by the rinse operation, the spin operation begins extracting additional liquid from the articles. During the spin operation, the washer basket rotates in one direction at a high angular velocity. This rotation creates a centrifugal force on the articles and the wash liquid causing excess liquid to exit or be extracted through perforations in the washer basket wall.
In order for the wash cycle to effectively clean the articles, it is necessary to ensure that the washing machine fills the washer basket and washer tub with an adequate amount of liquid such as water for agitation. If the amount of water provided is too low, then the articles might not have enough water to effectively clean the articles. In addition, too low of a water level will result in a large amount of mechanical stress on the agitator and its drive system (i.e., motor, transmission, and pulley, brake and clutch system). Furthermore, if there is a low level of water, then the articles cannot move as well which increases the possibility of damage to the articles. On the other hand, if there is too much water, then some of the articles will float in the washer basket and not receive enough interfacial wash action from the agitator to effectively clean the articles. Too much water is also energy inefficient because water is being wasted along with energy expended to heat, pump, and agitate the extra water. Another problem with adding too much water is that the agitator will not be able to impart the proper amount of back and forth motion to the articles for optimal cleaning or rinsing.
One approach used to overcome the above problems is to automatically control the amount of water added to the washer basket and washer tub during a wash cycle with an adaptive fill controller. In this approach the adaptive fill controller monitors the change in the phase angle of the motor while the washing machine is simultaneously filling with water and agitating. In order for the adaptive fill controller to work properly, the flow rate of water into the washing machine needs to be relatively constant. Generally, the flow rate of the water into the washing machine is not constant. Running a dishwasher or flushing a toilet while using the washing machine are some possible examples that may cause the flow rate of water to vary.
Typically, placing a flow restrictor in the housing of the water valves or inline with the water flow can provide a relatively constant flow rate. The flow restrictor is a pliable device that constricts an orifice as water pressure increases. The nominal flow rate when using a flow restrictor is about 6 gallons per minute even though the house water pressure might vary from 20 psi to 100 psi. One problem with the flow restrictor is that it degrades with time as the restrictor becomes less pliable. Other reasons for degradation include partial clogging of the orifice due to small particulates of sand or other foreign objects in the water supply. Another problem with the restrictor is that it is less effective as the water pressure drops below 20 psi which could occur in a house that uses well water with limited availability. Accordingly, there is a need to be able to compensate for varying flow rates without have to use a flow restrictor.